This invention relates to a blow-by gas separator and more particularly to an improved separation system for use with internal combustion engines in connection with crankcase gas recirculation.
In order to improve the emission qualities of internal combustion engines, they have been provided with recirculated crankcase ventilation systems wherein the blow-by gases from the crankcase are returned to the combustion chambers for further combustion of undesirable constituents such as hydrocarbons. The conventional type of system employs a combined oil separator and oil return device that receives the crankcase gases and separates oil from them with the separated oil being returned to the crankcase chamber. The thus purified crankcase gases are then delivered to the induction system for introduction into the combustion chambers wherein any unburned hydrocarbons that have not been separated can be reduced by further combustion.
FIGS. 1 through 3 are cross sectional views taken through a portion of the induction system utilized in conventional engines wherein the crankcase ventilation system is shown partially and identified generally by the reference numeral 21. The crankcase ventilation system 21 includes an oil separator, indicated generally by the reference numeral 22. This oil separator 22 is positioned in a first conduit 23 that receives crankcase gases from the crankcase ventilation system via a positive crankcase ventilation valve, which is not shown in this figure, in the flow direction indicated by the arrow A in FIG. 1.
The oil separator 22 is comprised of an outer housing that defines an oil separating chamber 24 which functions to remove oil from the blow-by gases in any suitable manner. In these and subsequent figures, a centrifugal type separator is depicted wherein the crankcase gases are delivered in a tangential direction to the chamber 24 so that the swirling will cause oil to deposit on the inner wall of the chamber. Of course, there are other types of oil separators with which this invention can be utilized.
The crankcase gases from which the oil is separated are then returned to the induction system through the conduit 21 and specifically through a return path 25 that flows in a direction indicated by the arrow B in FIG. 1. At the lower end of the separation chamber 24, there is provided an oil accumulating or oil return chamber 26. This chamber 26 communicates with the lower part of the separator 24 through a flow opening 27, which is valved by a drain valve 28. The drain valve 28 is pressure responsive and opens and closes in response to differences in the pressure in the chambers 24 and 26 (intake pressure and crankcase pressure).
The oil return chamber 26, in turn, has a discharge opening that communicates with the crankcase chamber through an oil return line 29. This opening is controlled by a pressure responsive valve 31, which, in most instances, is of the duck bill type and will open in response to pressure differences between the oil reservoir 26 and the oil return line 29.
Basically, the theory of operation is that as the engine is running, oil will be separated in the oil separator chamber 24 and under some running conditions will flow to the return chamber 26 when the pressure responsive valve 28 is opened as shown in FIG. 1. Under other running conditions, the pressure in the oil return chamber 26 will be greater than the pressure in the crankcase chamber and return line 29 and the check valve 31 will open and the oil will be returned to the crankcase.
However, the desired performance does not always occur under all running conditions and with all engines, particularly with engines where pressure in the induction system can at times be greater than atmospheric. This happens with supercharged engines of various forms such as turbocharged engines although it may occur in other types of engines as well.
The problem with this type of construction can be best understood by reference to FIGS. 1 through 3 with FIG. 1 showing the condition in a normal engine having a pressurized induction system such as a turbocharged engine when operating at idle. FIG. 2 shows the condition when operating under full load with the throttle open. FIG. 3 shows how the problem can arise with this type of construction.
Referring first to FIG. 1, when the engine is operating at idle, the crankcase ventilating gases from the PCV valve are delivered through the conduit 23 to the separator chamber 24 as shown by the arrow A. When this occurs, the pressure in the intake manifold is in the range of −70 to −60 kPa. At that time, the pressure in the crankcase chamber and the conduit 29 will be in the range of −0.2 to 0 kPa. Thus, under this condition, the pressure in the crankcase chamber is always higher than the pressure in the intake chamber and hence, the pressure responsive valve 28 will be opened and oil can flow through the passage 28 to accumulate in the oil return chamber 26 as shown by the shaded area indicated in the oil in this figure. As a result, no oil will be accumulating in the separator chamber 24 and oil free crankcase ventilating gases will be returned to the induction system so that any hydrocarbons that are present can be burned by further combustion in the combustion chamber.
As the load on the engine increases and the throttle valve is opened, the pressure in the intake manifold and hence, conduit 23 can rise to pressures in the range of −50 to +90 kPa. Under the same conditions, the crankcase chamber pressure ranges from −6.5 to +0.5 kPa. When this occurs, the check valve 28 will close as shown in FIG. 2 and when the pressure in the crankcase chamber is below the trapped pressure in the oil reservoir chamber 28, the drain check valve 31 will open and oil can flow to the crankcase. This does not occur, under all running conditions, however.
Thus, there may exist a condition where oil has been accumulated in the return chamber 26 as shown in FIG.1, but the pressure in the induction system is high enough to close the pressure response valve 28 before the drain check valve 31 has had a chance to open. As a result, further oil will accumulate in the separator chamber 24 and this oil can then pass into the induction system, a condition which is not desirable.
It is, therefore, a principal object to this invention to providean improved crankcase ventilation system including an improved blow-by gas separator wherein it will be insured that oil cannot accumulate in the separator chamber under any running conditions so that the oil is totally precluded from being able to pass into the induction system.